Many articles, documents, products and the like are currently marked with machine-readable indicia. Machine-readable indicia are used to carry a variety of information. Bar codes attached to a retail article being offered for sale, for example, are commonly used to carry pricing and related data. The subsequent storage of such data in a computer-readable database facilitates the performance of several useful applications such as inventory tracking, item tracking, customer tracking and so forth. In addition, machine reading of such data is considered to be more efficient and accurate than keyed data entry requiring a human operator to manually type the data into a database.
In many marking applications, a label containing a machine-readable indicia is attached or adhered to the item being marked. In a label-less marking application, a machine-readable indicia is associated with an item by depositing ink onto the surface of the item being marked. For several types of articles, however, such marking methods are not suitable. Some items, for example, may be too small to mark with a label, some items may not have sufficient surface area available for the addition of a label, some items may be intended for use in environments that can cause the loss or degradation of the label or deposited ink, and some items may be made of a material that is not suitable for the attachment of a label or for the absorption of ink. Further, the use of labels or inks is not suitable in situations where the label or ink may come off of the item and detrimentally contaminate a process or article with an adhesive, paper or ink.
In situations where it is not feasible to mark an item via a label or other traditional method, it is frequently possible to use a technique known as direct part marking (DPM) to form an embedded indicia directly into the item being marked. Thus, in direct part marking applications, the machine-readable indicia is formed directly into the item. For example, if the item to be marked is made of a metal or a plastic, the machine readable indicia is formed directly into the plastic or metal that constitutes the item.
The material from which the item is made, which is also the material from which the indicia is formed, is referred to herein as the “substrate.” The substrate can be a metal, glass, plastic, silicon or any of a wide variety of other materials. The indicia that is formed from the substrate will be referred to herein as an “embedded indicia.”
The embedded indicia can use, for example, a one or two-dimensional machine-readable coding scheme to store and communicate its data. The embedded indicia can be formed using several different methods. Substrate marking methods include, for example, the use of laser peening, laser etching, pin stamping, ink-jet printing, traditional peening, dot marking, scratching, sandblasting, machining, chemical etching, electrical arc pencil, embossing, vibration etching, welding, and cast, forge or mold engraving.
When an embedded indicia has been formed from, or into, a substrate in a DPM application, the indicia takes on a three-dimensional character. This is true even though the underlying coding scheme can be a coding scheme commonly referred to as a one or two-dimensional coding scheme. The Data Matrix code is an example of a two dimensional code used as an embedded indicia in DPM applications. The Data Matrix identification symbol is described in an AIM International Inc. technical specification entitled “International Symbology Specification—Data Matrix.” A variety of other coding schemes are also used in direct part marking applications. Other coding schemes used in DPM applications include PSOCR, OCRA, OCRB, Code 39, Code 128, UPC, Interleave 2 of 5 and PosiCode to list but a few.
Non-embedded machine-readable indicia, such as indicia carried on a label or printed directly onto an item, contain definite areas of differing reflectivity that represent and communicate data. The areas of differing reflectivity are read by using an optical reader. A wide variety of optical readers exist. Some optical readers operate by scanning the indicia with a laser light and sensing the light energy reflected to the reader by the indicia. These scanning-type readers can use a one-dimensional light sensor to detect the reflected light energy. Other optical readers use other types of light sources to illuminate the indicia. Further, some optical readers use a two-dimensional charge-coupled device (CCD) to sense reflected light. Further, optical reader units are sometimes constructed as a module or component that can be included in a hand-held portable computer to give it indicia reading capability. Optical readers also often include radio-frequency communication and display capabilities. The various types of traditional optical readers are not capable, however, of reading embedded indicia.
Readers capable of reading embedded indicia have been developed. As with the more traditional style readers described above, these readers include sensors to detect light that has been reflected from an indicia being read. The embedded indicia, however, since it is formed into the substrate of an item being marked, does not necessarily include areas of differing reflectivity sufficient for optical reading. Therefore, current embedded indicia readers create areas of differing reflectivity on the embedded indicia by directing light onto the three-dimensional indicia in a manner calculated to create shadows thereon. The contrast between the shadowed and non-shadowed portions of the area containing the embedded indicia creates the differences in reflectivity that can then be detected by the light energy sensor of the reader.
In order to create readable shadows, current readers of embedded indicia illuminate the indicia in a manner calculated to create shadows and thus contrast on the embedded indicia. This is depicted in FIG. 1. A light generator 100 directs light energy 102 through a first window 103 and toward an embedded indicia 104. The light energy is reflected 106 by the embedded indicia 104. The reflected light energy 106 passes through a second window 107 in the housing and toward a light sensor 108. The light sensor 108 is located separately from the light generator 100 in the housing. Compared to the location of the light generator 100, the light sensor 108 is positioned more directly above the indicia 104. The low angle 110 of the generated light energy 102 relative to the plane of the embedded indicia 104 creates shadows on the embedded indicia and thus adds the areas of differing reflectivity that can be detected by the light sensor 108.
The significant separation required between the light generator and the light sensor creates several problems and limitations when designing an embedded indicia reader. These problems are compounded if the embedded indicia reader is to be a hand-held reader. First, for example, the housing of the reader requires two separate windows, one window permitting generated light energy to exit the reader and a second window permitting the reflected light energy entering the reader to be sensed. The need for two windows increases the complexity of the manufacturing process. In addition, both windows must be specially sealed so that environmental contamination from dust, moisture, etc, cannot enter the housing and damage internal components. Second, the need to separate the light generator from the light sensor within the housing requires that the reading system include at least two independent components that must be separately installed and coupled to the system. In a reader containing several components such as a radio transceiver, infrared transceiver and/or user removable components, etc., some of which may even interfere with each other, the need to separately and specially locate the light generator and light sensor can further increase the complexity of the design task.
Third, the “shadow” style of reading requires two distinct and unobstructed light pathways between the housing and the embedded indicia. There must be a first clear pathway from the light generator to the indicia and a second clear pathway from the indicia to the light sensor. This means that the housing and its internal components must be designed so as to not interfere with either path. Further, in a hand-held unit, the unit must be designed so that it can be held and directed toward the indicia in a manner such that the user's hand will not block either of the paths. Complexity is further increased if the hand-held reader is to be a small, lightweight, portable unit that in some instances might be desired to be roughly equivalent to or smaller than the size of the hand holding it.
Consequently, a new style of embedded indicia reader is needed that avoids some or all of the limitations and requirements of the shadow-style reading system described above. For example, it is desired to develop an embedded indicia reader that can use a single port for both the outgoing transmission of light energy and for the incoming reception of the reflected signals. It is desired to develop an embedded indicia reading system that can send and receive light energy via generally the same pathway between the reader and the indicia. By way of further example, it is additionally or alternatively desired to create an embedded indicia reading component that can be added to an embedded indicia reader as a single integrated component capable of both generating the light energy and sensing its reflection from the indicia. Additionally, it is believed that a review of this specification, including its claims and drawings, will reveal and imply additional deficiencies of the prior systems that are improved or remedied by the inventions disclosed herein.